A surprising property of electrical spread in the network of rods in the turtle's retina.

Flashing a localised stimulus onto a turtle's retina produces an intracellular potential wave which spreads through electrical connections from illuminated to unilluminated photoreceptors. The response in unilluminated rods (but not in cones) becomes faster as the distance from the source increases, perhaps because voltage-dependent permeability changes in the rod membrane make the coupled network behave like a high-pass filter.